Ribeiro Junior Luiz Antonio, Stafström Sven
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden.
Phys Chem Chem Phys. 2017 Feb 1;19(5):4078-4084. doi: 10.1039/c6cp07478b.
Polaron dynamics in anisotropic organic molecular semiconductors is theoretically investigated and simulated in the framework of a semi-classical Holstein-Peierls model. Our computational protocol is presented and applied to studies of a two-dimensional molecular crystal. The intermolecular (Peierls) parameters for a particular crystal direction are systematically changed in order to study the effect of anisotropy in the system. The usefulness of this methodology is highlighted by studying the polaron dynamics on a picosecond timescale, which provides a microscopic insight into the influence of the interplay between different intramolecular parameters on the charge transport mechanism. Our results show that the polaron mobility is substantially reduced in going from an anisotropic to an isotropic relationship between the Peierls parameters for different directions in the crystal. Interestingly, the molecular charge distribution presents three different signatures corresponding to a one-dimensional polaron, a two-dimensional polaron, and an intermediate state for which the polaron localization depends on the degree of anisotropy. Importantly, the two-dimensional polaron, which is present in the essentially isotropic system, is immobile whereas the other two types of polarons are mobile. This, in order for polaron transport to occur in a two-dimensional molecular based system, this system has to be anisotropic.
在半经典的霍尔斯坦 - 佩尔斯模型框架内，对各向异性有机分子半导体中的极化子动力学进行了理论研究和模拟。我们展示了计算方法并将其应用于二维分子晶体的研究。为了研究系统中各向异性的影响，特定晶体方向的分子间（佩尔斯）参数被系统地改变。通过研究皮秒时间尺度上的极化子动力学突出了该方法的实用性，这为深入了解不同分子内参数之间的相互作用对电荷传输机制的影响提供了微观视角。我们的结果表明，当晶体中不同方向的佩尔斯参数从各向异性关系变为各向同性关系时，极化子迁移率大幅降低。有趣的是，分子电荷分布呈现出三种不同特征，分别对应一维极化子、二维极化子以及极化子局域化取决于各向异性程度的中间态。重要的是，存在于基本各向同性系统中的二维极化子是不动的，而其他两种类型的极化子是可移动的。因此，为了使极化子在二维分子基系统中发生传输，该系统必须是各向异性的。
